There have been a couple of decent articles in the last few days regarding studies that show that running on soft surfaces (say, dirt instead of pavement) and more cushioned shoes don't really have any effect on whether runners get injured. Gina Kolata seems to have started it off in the New York Times with her article "For Runners, Soft Ground Can Be Hard On The Body." Amby Burfoot at Runner's World gives it his spin as well, with "If Grass and Shoe Cushioning Can't Prevent Injuries, What Can?"
Both articles are worth a read - I'd encourage you all to take a look.
Outside Magazine weighs in as well...
And the Beer Runner puts in his always awesome two cents.